# pygame / include / pgJointObject.h

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57``` ```/* pygame physics - Pygame physics module Copyright (C) 2008 Zhang Fan This library is free software; you can redistribute it and/or modify it under the terms of the GNU Library General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public License for more details. You should have received a copy of the GNU Library General Public License along with this library; if not, write to the Free Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */ /** * Joint solve algorithm * Velocity after free updating may violate joint constraint, * Solve joint velocity to set velocity right, * body position may violate joint constraint by error accumulation and discrete time step simulation, * so body position must be corrected. * ********************* * Distance joint solve method * joint anchor velocity is vp, body velocity is vb, body angular velocity is wb,the vector between body anchor * to body center is l * vp = vb + cross(wb,l) * d(vp) = d(vb) + cross(d(wb),l) * I is the impulse which joint gives to body. I = m*d(vb), cross(I,l) = Interia*(wb) * the constraint is distance(anchor1-anchor2) = constant,it can apply this: * project((vp1 - vp2),(anchor1-anchor2)) = 0 * so,we can solve it by the above equations. */ #ifndef _PHYSICS_JOINT_H_ #define _PHYSICS_JOINT_H_ /** * Solve the joint constraints. * * @param joint * @param stepTime */ int JointObject_SolveConstraints (PyJointObject *joint, double stepTime); /** * Python C API export hook. * * @param c_api Pointer to the C API array. */ void PyJointObject_ExportCAPI (void **c_api); #endif /* _PHYSICS_JOINT_H_ */ ```
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